Theoretical and experimental investigations of ultrafiltration (UF) of albumin solutions were conducted with a batch stirred cell. The theoretical model predicted that the limiting flux u∞ is equal to (K'm/ø), where K'm is the effective mass transfer coefficient and ø is the rejection coefficient. This interesting finding simply says that the limiting flux is independent of the pressure applied as was observed by many workers. Also, the limiting flux u∞ was theoretically found to increase with the stirring speed and decreases with the bulk protein concentration which is consistent with previous experimental findings. Experimental studies confirmed these predictions. Albumin ultrafiltration rate appears to be limited by the increased adsorption rate of the protein on the membrane surface and onto the pores of the membrane.